Recurring Events

Recurrence rules allow events to recur, for example for a weekly meeting, or an anniversary. This is done with the RRULE and RDATE property. The RRULE property allows for a LOT of different rules. VObject has support for a lot of them, but not all.

To read more about RRULE and all the options, check out RFC5545. VObject supports the following options:

  1. UNTIL for an end date,
  2. INTERVAL for for example "every 2 days",
  3. COUNT to stop recurring after x items,
  4. FREQ=DAILY to recur every day, and BYDAY to limit it to certain days,
  5. FREQ=WEEKLY to recur every week, BYDAY to expand this to multiple weekdays in every week and WKST to specify on which day the week starts,
  6. FREQ=MONTHLY to recur every month, BYMONTHDAY to expand this to certain days in a month, BYDAY to expand it to certain weekdays occuring in a month, and BYSETPOS to limit the last two expansions,
  7. FREQ=YEARLY to recur every year, BYMONTH to expand that to certain months in a year, and BYDAY and BYWEEKDAY to expand the BYMONTH rule even further.

VObject supports the EXDATE property for exclusions, and RDATE as well.

This is an example of a meeting that happens every 2nd monday of every month:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Sabre//Sabre VObject 2.0//EN
BEGIN:VEVENT
UID:1102c450-e0d7-11e1-9b23-0800200c9a66
DTSTART:20120109T140000Z
RRULE:FREQ=MONTHLY;BYDAY=MO;BYSETPOS=2
END:VEVENT
END:VCALENDAR

To figure out all the meetings for this year, we can use the following syntax:

$vcalendar = VObject\Reader::read($data);
$newVCalendar = $vcalendar->expand(new DateTime('2012-01-01'), new DateTime('2012-12-31'));

What the expand method does, is look at its inner events, and expand all the recurrence rules. Then, it returns a new calendar that has all its events expanded.

This new calendar now contains 12 events. The first will have its RRULE stripped, and every subsequent VEVENT has the correct meeting date and a RECURRENCE-ID set.

This results in something like this:

BEGIN:VCALENDAR
  VERSION:2.0
  PRODID:-//Sabre//Sabre VObject 2.0//EN
  BEGIN:VEVENT
    UID:1102c450-e0d7-11e1-9b23-0800200c9a66
    DTSTART:20120109T140000Z
  END:VEVENT
  BEGIN:VEVENT
    UID:1102c450-e0d7-11e1-9b23-0800200c9a66
    RECURRENCE-ID:20120213T140000Z
    DTSTART:20120213T140000Z
  END:VEVENT
  BEGIN:VEVENT
    UID:1102c450-e0d7-11e1-9b23-0800200c9a66
    RECURRENCE-ID:20120312T140000Z
    DTSTART:20120312T140000Z
  END:VEVENT
  ..etc..
END:VCALENDAR

In a recurring event, single instances can also be overriden. VObject also takes these into consideration. The reason we needed to specify a start and end-date, is because some recurrence rules can be 'never ending'.

You should make sure you pick a sane date-range. Because if you pick a 50 year time-range, for a daily recurring event; this would result in over 18K objects.

Note: Before sabre/vobject version 4, the expand() method did not return a new calendar, but it edited the entire calendar in-place. So from version 4 to retrieve a calendar with only those events in the given period, you have to use the object returning from expand() (e.g. $vcalendar = $vcalendar->expand(new DateTime('2012-01-01'), new DateTime('2012-12-31'));).